Abstract

Ubiquitously expressed genes contain regulatory features which allow expression in virtually all cell types. In an effort to understand the molecular basis for this regulatory feature, the chromatin structure of the murine adenosine deaminase gene was examined by DNase I digestion in nuclei of several tissues. The promoter contained a strong hypersensitive site in all tissues examined, including those with very high and very low levels of ADA expression. Transgenic mouse studies revealed that a 3.3 kbEcoRI (3.3 EE) fragment from intron I was required to generate a strong promoter DNase I hypersensitive site, and to produce ubiquitous expression. The 3.3EE fragment also contained a thymic enhancer activity which mapped to sequences conserved with the human ADA gene T-lymphocyte enhancer. Mutational analysis indicated that ubiquitous expression was not dependent on the presence of a functional thymic enhancer. Both the thymic enhancer and the ubiquitous activator within the 3.3EE fragment functioned with heterologous promoters in transgenic mice.